For me, the choice simply boils down to this: how easy is it to write something in Perl, and in Java? In my experience, Java is very verbose, with lots and lots of explicit layers (converting strings to byte buffers to ...) that you don't need in Perl, so you can easily end up with 2-3 times the amount of code in Java than in Perl.

So I recommend the approach as advocated by Aristotle: write a significant part both in Perl an in Java, and compare how hard it was, how big the code is, how feature rich, and how many bugs you can find. For good measure, It'd throw in a few more languages, at the very least, Python. That way, you will not give the impression of being a stubborn hardhead, and people will be more willing to listen to your arguments. And, you and your people might like it.